There is a great deal of prior art describing the preparation of overbased colloidal products and the transformation of such products aimed at incorporating certain elements such as sulphur, phosphorus and/or boron into them.
Thus, for example, our French patent FR-B-2 645 168 describes thio-phosphorous compounds obtained by reacting at least one overbased compound with a phosphorus sulphide. The overbased compound can consist of an alkali or alkaline-earth metal salt of an acid such as a sulphonic acid, overbased by treating a reaction mixture containing that salt and at least one alkali metal or alkaline-earth metal oxide or hydroxide with a weak acid such as carbon dioxide. More particularly, the overbased compound can consist of a calcium sulphonate overbased by calcium carbonate. The overbased compound thus defined is reacted with a phosphorus sulphide such as P.sub.4 S.sub.7, P.sub.4 S.sub.9 or P.sub.4 S.sub.10, generally used in a proportion of 0.002 to 0.15 moles of phosphorus per base equivalent.
We have now discovered that colloidal thio-phosphorous products with improved properties can be prepared from lime Ca(OH).sub.2 in a colloidal form rather than from an alkali or alkaline-earth metal carbonate.
Colloidal lime has been described in our French patent application FR-A-2 722 117.
The thio-phosphorous products of the invention can generally be defined by the fact that they are the result of carrying out a process comprising the following steps:
a) adding at least one phosphorus sulphide to colloidal lime in the presence of at least one volatile organic solvent; PA0 b) heating with stirring to a temperature which can be, for example, up to the reflux temperature of the volatile solvent; and PA0 c) eliminating the volatile solvent, for example using reduced pressure. PA0 aliphatic hydrocarbons, such as hexanes or heptanes; PA0 cycloaliphatic hydrocarbons, such as cyclohexane; PA0 aromatic hydrocarbons, such as toluene or xylenes; PA0 halogenated hydrocarbons, for example chlorinated hydrocarbons such as monochloro- or dichlorobenzene, or dichloro- or trichloroethane; or PA0 heterocyclic compounds such as tetrahydrofuran.
Colloidal lime can be prepared, for example, as described in French patent application FR-A-2 722 117 cited above, by reacting calcium oxide or hydride or calcium metal with water in an organic medium and in the presence of a surfactant, for example a calcium alkylarylsulphonate.
Organic media in which the colloidal lime can be formed in step a) are:
The surfactant can be an alkylarylsulphonate of an alkali metal (sodium or potassium) or an alkaline-earth metal (magnesium, calcium or barium). It is usually a calcium alkylarylsulphonate. In the latter case, the alkylarylsulphonate can be formed in situ by reacting an alkylarylsulphonic acid with the calcium hydroxide formed in the medium.
The reaction can advantageously be carried out in the presence of a promoter, for example an aliphatic mono-alcohol such as methanol. It can also be carried out in a mineral or synthetic diluting oil. The reaction temperature is generally in the range 0.degree. C. to 80.degree. C., normally in the range 5.degree. C. to 45.degree. C.
The colloidal lime prepared generally has a calcium content whice can be as much as about 35% by weight with respect to the active matter (core of the micelle constituted by calcium hydroxide+surfactant, excluding any diluting oil). The basicity reserve of the product in its diluted form in an oil at a concentration of 30% to 60% by weight of active matter corresponds to a TBN (Total Base Number) of about 100 to 500, normally 200 to 400 mg of potassium hydroxide per gram of product. The structure of the lime constituting the core of the micelle is confirmed by infra-red analysis.
Finally, the sulphur content of the product, which originates from the alkylarylsulphonate used as the surfactant, can be, for example, 1% to 5% by weight with respect to the active matter.
In step a) of the process for the production of thio-phosphorous products of the present invention, a phosphorus sulphide such as P.sub.4 S.sub.7, P.sub.4 S.sub.9 or P.sub.4 S.sub.10, more particularly tetraphosphorus decasulphide P.sub.4 S.sub.10, is added to the colloidal lime, for example in a proportion corresponding to a phosphorus to calcium atomic ratio of 0.1 to 2.5, preferably 0.5 to 2. The colloidal lime is generally in the form in which it is obtained from the process described in French patent application FR-A-2 722 117, i.e., the composition used comprises at least one surfactant, in general a calcium alkylarylsulphonate, a volatile organic liquid, more particularly selected from those mentioned above, and a diluting oil.
Then in step b), the reaction mixture is heated with stirring, for example to the reflux temperature of the volatile solvent.
In step c), it is heated under reduced pressure to eliminate the volatile solvent.
The products of the invention are colloidal products which are in the form of inverse micelles (water-in-oil), for example at a concentration of 30% to 60% in the diluting oil used. At these concentrations, they can have a sulphur content of 1% to 15% by weight and a phosphorus content of 0.2% to 7% by weight.
They are soluble and stable in both mineral and synthetic lubricating oils, in which they can be used as anti-wear and extreme pressure additives. To this end, they can be used at concentrations of 0.5% to 20% by weight, preferably 1% to 5% by weight, for example.